Uncertainty cuts both ways highlights University of Bristol’s Stephan Lewandowsky – if your preferred estimate is at the low end of a range, you’re neglecting similarly likely high end estimates. Image credit: University of Bristol

These messages could hardly be any clearer, but still some of us remain uncertain on the need to act. The best argument for waiting until we’re more certain to act is that if climate change turns out to be harmless, our efforts to fight it will be wasted. Even simple things like current weather are enough to sway our opinions, and when uncertain it’s always tempting to feel like we don’t need to do anything. But that’s the wrong reaction to uncertainty on climate change, according to psychologist Stephan Lewandowsky from the University of Bristol, UK.

A Roman altar with the Sun in its chariot on the left, and Vulcan, the god of fire and volcanoes on the right. The climate gods long favoured the Roman Empire, with Earth’s orbital dance credited for increasing the amount of solar energy falling on Earth at the time. Image copyright: Nick Thompson, used via Flickr Creative Commons License.

Our climate has changed before. It’s something most of us realise and can agree on and, according to Skeptical Science, it’s currently the most used argument against human-caused warming. If such changes have happened naturally before, the argument goes, then surely today’s warming must also be natural. It’s an appealing idea, with an instinctively ‘right’ feel. Nature is so huge compared to us puny humans, how can we alter its course? The warming we’re measuring today must just be a natural fluctuation.

It’s such an appealing argument that at the beginning of the 20th century that’s just what many scientists thought – that humans couldn’t alter Earth’s climate. In the time since, our knowledge has come a long way. We’ve explored space, become able to build the electronics that are letting you read this, and climate science has likewise advanced and benefited from these advances.

So what do we know today that might convince the sceptical scientists of 115 years ago that we’re warming the planet? Recently, Richard Mallett, one of my Twitter friends who describes himself as sceptical about mainstream climate science, made a point that serves as an excellent test of our current knowledge:

@andyextance Climate science should be able to explain the Holocene, Roman, Medieval and current warmings and the cold periods in between.

Of the historical warmings he’s referring to, perhaps the least familiar is the Holocene, which is ironic, as the Holocene is now. It’s the current period of geological time that started at the end of the last ice age, 11,700 years ago. By 1900 scientists would have known the term, but they couldn’t explain why it wasn’t as icey as before.

Three variables of the Earth’s orbit—eccentricity, obliquity, and precession—affect global climate. Changes in eccentricity (the amount the orbit diverges from a perfect circle) vary the distance of Earth from the Sun. Changes in obliquity (tilt of Earth’s axis) vary the strength of the seasons. Precession (wobble in Earth’s axis) varies the timing of the seasons. For more complete descriptions, read Milutin Milankovitch: Orbital Variations. Image credit: NASA/Robert Simmon.

The explanation we have today comes thanks to the calculations Milutin Milanković worked out by hand between 1909 and 1941. Milutin showed that thanks to the gravitational pull of the Moon, Jupiter and Saturn, Earth’s orbit around the Sun varies in three ways. Over a cycle of roughly 96,000 years our path varies between more circular and more oval shapes. The other two ways come because Earth’s poles are slightly tilted relative to the Sun’s axis, which is why we have seasons. The angle of that tilt shifts over a roughly 41,000 year cycle. Earth also revolves around that tilted axis, like a spinning top does when it slows down, every 23,000 years.

“How many of you think the world is cooling?” That’s what Steve Schneider asked the studio audience of the Tonight Show with Johnny Carson in September 1977. And when the majority put their hands up, he explained that the recent cooling trend had only been short-term. Though the unscripted poll meant Steve wasn’t invited back to the programme, through the summer of that year he had brought climate science to US national TV. The appearances typified Steve’s efforts to bring climate change to the world’s notice – efforts that would later draw attention of a less desirable sort.

Building on his earlier high profile research, Steve had just published ‘The Genesis Strategy: Climate and Global Survival’, predicting ‘demonstrable climate change’ by the end of the century. Whether human pollution would cause warming or cooling, he argued governments should copy the biblical story where Joseph told Pharoah to prepare for lean years ahead. In a decade already torn by rocketing food and oil prices, the advice resonated with many who wanted to head off any further crises.

Some scientists criticised Steve and those like him for speaking straight to the public. In particular, climate science uncertainties were so great that they feared confusion – like that over whether temperatures were rising or falling – was inevitable. That dispute grew from a basic question about science’s place in society. Should researchers concentrate on questions they can comfortably answer using their existing methods? Or should they tackle questions the world needs answered, even if the results that follow are less definite?

At a meeting to discuss climate and modelling research within the Global Atmospheric Research Programme (GARP) in 1974 near Stockholm, Sweden, Steve pushed for the second approach. Given the food problems the world was struggling with at the time, it seemed obvious that climate change impacts like droughts, floods and extreme temperatures would bring famines. “I stood alone in arguing that we had to consider the implications of what we were researching,” Steve later wrote. While some attacked him angrily, saying they weren’t ready to address these problems, conference organiser Bert Bolin agreed that socially important questions must be answered.

The suggestion was also controversial because it meant blurring the lines between climate science and other subjects, such as agriculture, ecology and even economics. The director at the US National Center for Atmospheric Research (NCAR) in Boulder, Colorado, where Steve worked, warned that crossing subject boundaries might cost him promotion. But he responded with characteristic wilfulness, founding a journal doing exactly what he was warned not to. Read the rest of this entry »

Jim Hansen (bottom left) and his family. For their benefit, and for the next generation as a whole, he is pushing for more urgent action on global warming. Credit: JimHansen

Even limiting human-made global climate warming to 2°C above preindustrial temperatures would subject young people, future generations and nature to irreparable harm, leading scientists said on Tuesday. The team led by pioneering climate researcher Jim Hansen, now at Columbia University in New York, calls aiming for this internationally-recognised threshold ‘foolhardy’. In a paper published in PLOS ONE, they outline a case for aiming for 1°C that supports efforts to sue the US government for not doing enough.

“Governments are blatantly failing to do their job,” Jim told me. “They know that human-caused climate change is beginning and poses a huge risk to young people and future generations, and they understand that we must phase out fossil fuel emissions. Yet they go right ahead encouraging companies to go after every fossil fuel that can be found!”

Tiny plants in Arctic Canada have shown that average summer temperatures there over the last 100 years are higher than those during any century for over 44,000 years. Gifford Miller from the University of Colorado, Boulder, and his teammates collected plants perfectly preserved but recently revealed by rapidly retreating ice sheets. The temperature findings are especially surprising as around 10% more energy from the sun fell on the Northern half of the planet 5,000 years ago than today. And by looking at other scientists’ historical temperature records, they think the last time temperatures were as warm as today was likely around 120,000 years ago. “This adds to the growing consensus that the greenhouse gases we’ve added to the atmosphere have made a very large difference to the planet’s energy balance,” Gifford told me.

Scientists have known receding glaciers on Baffin Island are revealing well-preserved moss and lichen for almost 50 years. Gifford first read about it during his PhD, which he completed in 1975, in a paper written by a Canadian Department of Mines and Technical Surveys employee in 1966. “I had been to that site in 1981, found where he’d built a camp at the ice edge, measured how far the ice had disappeared and found plants coming out,” he recalled. “I’d repeated what he had done, but hadn’t done anything else with it. But as the ice is melting a lot right now we hypothesised that this wasn’t an isolated case.”

Glaciers don’t usually preserve what’s underneath them. “It’s almost counterintuitive to some people – you think of ice doing some damage to the landscape,” Gifford said. “But ice doesn’t move on its own, it’s driven by gravity. Where it’s flat, there’s not a whole lot of gravity pushing it, and if the ice is fairly thin and cold it’s an exquisite preservation agent. They’re frozen solid when they’re under the ice, which is very cold, like -14°C.” Sites like that can be hard to get to, as many are on plateaus high above Baffin Island. “You could mount climbing expeditions and spend a week getting to one site, so really there’s no practical way to get up there, except to have very good weather and a helicopter,” the scientist added. Read the rest of this entry »

Woods Hole Oceanographic Institution’s Jessica Tierney has patiently produced a record of rainfall in East Africa reaching back 40,000 years, from sediment collected from pirate- and extremist-infested waters. Image copyright: Tom Kleindinst, Woods Hole Oceanographic Institution

Having dodged pirates and extremists, and slogged for two years to interpret the record collected, US scientists have shown how abruptly rainy climates in East Africa come and go. Jessica Tierney puzzled out a rainfall record back to the last ice age from mud collected in one of the last research cruises to brave the Horn of Africa. “The region goes from being pretty humid to very arid in hundreds of years,” Jessica, who works at Woods Hole Oceanographic Institution (WHOI) in Massachusetts, told me. “That’s important because there’s a threshold behaviour in its rainfall. We need to better understand what drives those thresholds, and when we’d expect to be pushed over one, as it has huge implications for predicting drought and famine in the region.”

Long interested in ancient East African climate, Jessica wanted to study the Horn of Africa area, which includes Ethiopia and Somalia, because the climate there is very sensitive and variable. But its dry conditions rule out many options scientists use to build historical records from ice, cave deposits, sediments from lake beds or tree rings. So in 2010, she started working with Peter deMenocal at Lamont-Doherty Earth Observatory in New York, who collected sea bed sediments from the area in April and May 2001.

“We boarded ship in Dar Es Salaam in Tanzania and our cruise was to end in Port Said, in Egypt,” Peter told me. That took the team down the Somali coast and into the Gulf of Aden, where a few months earlier suicide bombers killed 17 sailors aboard the USS Cole. Though the scientists were worried, the captain of their Dutch research ship, R/V Pelagia was vigilant. “He had ordered radio silence, and we actually turned off all our lights on the ship at night, even navigation lights,” Peter recalled. “He had also put in orders for us to train on what to do in case we were boarded.”

On the wall of Wally Broecker’s building at the Lamont-Doherty Earth Observatory hangs a 16-foot long terry-cloth snake, blue with pink spots, that he calls the ‘climate beast’. Left in his office as a surprise by his workmates, its name refers to one of Wally’s most powerful quotes about the climate: “If you’re living with an angry beast, you shouldn’t poke it with a sharp stick.”

Today, the sharp stick is the CO2 we’re emitting by burning fossil fuels, which Wally was warning about by 1975. By that time he had also helped confirm that throughout history, changes in Earth’s orbit have given the climate beast regular kicks, triggering rapid exits from ice ages. He became obsessed with the idea that climate had changed abruptly in the past, and the idea we could provoke the ‘angry beast’ into doing it again.

Among the many samples that Wally was carbon dating, from the late 1950s onwards he was getting treasure from the oceans. Pouring sulphuric acid into seawater, he could convert dissolved carbonate back into CO2 gas that he could then carbon date. And though nuclear weapon tests had previously messed with Wally’s results, they actually turned out to help improved our knowledge of the oceans. The H-bomb tests produced more of the radioactive carbon-14 his technique counts, and as that spike moved through the oceans, Wally could track how fast they absorbed that CO2.